1. Field of Invention
The invention relates generally to the field of computer graphics and graphics computer systems. More specifically, the invention relates to texture mapping circuits for use in graphics systems.
2. Background Information
Prior art graphics systems, including those implemented on engineering workstations, which often have a dedicated graphics subsystem, typically include texture mapping hardware. Traditionally texture mapping has been used to add realism to computer graphics images.
In its basic form, texture mapping lays an image onto an object. The image (texture image) is stored in a texture memory (texture space) addressed by (S,T,R) texture coordinates. The texture image is mapped to the object's surface by dividing the object's surface into polygons. For each polygon the vertices defined in terms of (X,Y,Z) coordinates are mapped into texture coordinates. The texture coordinates are used to index into the texture image stored in the texture memory. The known texture coordinates, derived from the polygon's vetices, are interpolated across the polygon to determine the texture image value at each of the polygon's picture elements ("pixels"). To map the texture image onto the object, the color of the object at each pixel is modified by the corresponding color from the texture image. When the polygon is viewed on the screen, a portion of the texture image is mapped onto the polygon. The end result of this texturing process is that the texture image covers the surface of the object.
While conventional texture mapping hardware performs texture interpolation, prior graphics systems have never before provided a path between input data and texture coordinates. In the past, the addresses for texture mapping would be formed by an iterator which iterates addresses along some predetermined planar slope to create the final (S,T,R) addresses. These (S,T,R) addresses are limited by the setup of the planar slope. This limitation in prior art system requires input geometry to be created before any sampling can begin with the texture image. Therefore, it is desirable to provide an apparatus and method for providing a path between input data and texture coordinates without requiring input geometry to be generated. It is also desirable to provide applications for this method and apparatus, such as color conversion, special effects like displacement addressing, and resampling along nonlinear surfaces using the method and apparatus of the present invention.